


Tenebrous

by Petrichora_Vellichor



Category: Supernatural
Genre: Angst, Blood, Dean is deep in denial, M/M, Mark of Cain (Supernatural), Pre-Slash, Somewhat canon divergent, Violent Thoughts
Language: English
Status: Completed
Published: 2019-03-02
Updated: 2019-03-02
Packaged: 2019-11-08 06:46:24
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 585
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17976377
Author URL: https://archiveofourown.org/users/Petrichora_Vellichor/pseuds/Petrichora_Vellichor
Summary: Set during 10x05, "Fan Fiction." Sam's teasing about Destiel triggers some disturbing thoughts for a Dean who is increasingly struggling to control the Mark of Cain.





	Tenebrous

**Author's Note:**

> **tenebrous** _(adjective)_ shut off from the light; dark

Sam, Dean thought as the two of them crossed the school parking lot to where Baby waited, really needed to fucking drop it.

“I mean, shouldn’t it be ‘Deastiel’?” Sam was saying, and Dean bit back the urge to shout. The Mark began to pulse painfully on his arm, sending surges so strong his fingers shook. 

_Unbidden, the image of Cas flittered into his mind. The angel was standing, alone and illuminated, shimmering softly in a beam of pale light surrounded by darkness. He was battered, bleeding, his blue eyes begging as he gazed into the surrounding shadows; when he spoke, his voice came out as a shuddering gasp. “Dean…”_

_Beyond the light, in the whirling blackness that filled the rest of his mind, Dean saw a more sinister version of himself take shape. He watched as the Darker Dean stepped forward, its mouth curled in a snarl, stalking slowly toward the light._

Back in the real world, Dean clenched his hand into a fist, forcing it to his side where Sam wouldn’t see. “Really?” he ground out, barely suppressing the bulk of his ire as he fixed Sam with a glare. “ _That’s_ your issue with this?!”

Sam, meanwhile, was too caught up in his own amusement to pick up on the danger in Dean’s tone. “No, of course that’s not my issue.” Then: “You know, how about ‘Sastiel’? ‘Samstiel’?”

**_Anger._ **

_Fiery._

_Furious._

_Dark._

_Demanding._

_In Dean’s mind, concern flooded Cas’s face, and Dean watched as the angel reached out to the Darker Dean, lips slipping silently over words that seemed to fill Dean’s more feral self with wild, blinding rage. The Darker Dean descended with a growl, eyes black, the First Blade glowing red in its grip._

_But Cas didn’t run, didn’t summon his sword from his sleeve. He just lowered his hand, watching, waiting, looking sad._

In the parking lot, Dean’s nails bit into his palm, drawing blood. The pain was good; it grounded him, allowed him to shove aside his imaginings so that he could think. “All right, okay,” he said, managing to keep his tone somewhat level as he addressed Sam, “you know what? You’re gonna do that thing where you just shut the hell up, forever.”

Sam laughed, and somehow, the sound was soothing. The pain of the Mark began to ebb, rendering Dean weak with relief. He and Sam talked a bit about the case–or rather, the apparent lack thereof–and Dean had just decided on dropping Sam off at the motel and then finding himself a bar to get good and drunk at when Sam quirked a brow and said it: “‘CasDean’?” 

The effect was instantaneous, ripping Dean from reality and throwing him back onto the darkened ground of his mind… 

_He landed hard, helpless and dazed, could only gasp as the Darker Dean darted forward with a hideous shriek, stabbing the Blade into Cas’s chest. Dean screamed, struggled to stand as Cas crumpled, lifeless, into the shadows…_

_The Darker Dean pivoted toward the sound. It fixed Dean with its blacked stare and, with a twisted smile, whispered, “Soon…”_

“SHUT YOUR FACE!” Dean shouted, and with a jolt, he found himself back in the parking lot, Sam staring at him in surprised concern.

“Dean…?”

Dean let out a shaky breath, cursing quietly. He palmed the handle of the Impala’s driver-side door, and the crimson blood from his hand left a red smear on the smooth blackness of Baby’s paint. “Shut your face, and get in the car.”

**Author's Note:**

> Tumblr version of this story, if you enjoyed it and feel like sharing. :) [Tenebrous](https://petrichoravellichor.tumblr.com/post/183135157332/tenebrous)
> 
> Kudos and/or comments are also greatly appreciated!


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